A reformer may convert a liquid fuel such as gasoline, diesel fuel, ethanol, etc. into a reformate gas so that the reformate gas can be combusted by an engine to improve combustion stability, knock resistance, and heating value. Further, reformed fuel may be used to purge or reduce constituents held or stored by an exhaust gas after treatment device. In one example, a reformate system may include a buffer tank, cooler, vaporizer, storage vessel, and gaseous injector to facilitate reformate use by a vehicle engine.
The inventor herein recognizes various issues that may develop with engine and reformate systems. For example, as the number and complexity of components in a reformate system increases, an engine may need to operate under conditions both with and without reformate. In an engine designed to utilize reformate gas, such modes may differ from those of conventional engines. In one example, a low supply of reformate gas could result in engine misfire. In a further example, a degradation of a reformate system component may lead to increased emissions or less efficient engine combustion. Therefore, the present description provides methods and systems for operating an engine utilizing reformate gaseous fuel are described. In one example, a method of operating an engine, comprising: limiting reformate flow to said engine in response to degradation of a fuel reformer; reducing an engine constituent proportionate to said limiting reformate flow; and increasing an amount of liquid fuel delivered to said engine to maintain engine torque and an air-fuel ratio of said engine prior to said limiting reformate flow.
One advantage of the above method is that consequences of reformate system degradation may be reduced by limiting use of the reformate system after degradation is detected. For example, if the reformate system is providing less than a threshold amount of reformate, reformer operation can be limited so that less energy is consumed by operating the reformer and so that the engine does not continue to operate as if a higher amount of reformate is available. Further, by adjusting liquid fuel supplied to an engine as well as engine constituents (e.g., charge dilution and/or boost) reasonable engine performance may be maintained. In this way, engine operation may be maintained at a reasonable level.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.